Shape memory material refers to a material that can sense the environmental change (e.g. temperature, force, electromagnetic, solvent, and other stimulus), and adjust its state parameters (e.g. shape, position, and strain) in response to such a change, so as to recover back to its preset state. Depending on different stimulus conditions, the shape memory material may be, for example, thermosensitive, photosensitive, electrosensitive, or chemically induced. At present, a variety of thermally sensitive shape memory polymers are developed through chemical and physical processes and come into use by researchers at home and abroad. However, the overall performance is generally less desirable. For the purpose of meeting the requirements for use in clinic in biomedicine, the thermally sensitive shape memory polymer needs to have a mild stimulus condition close to the body temperature or adaptable to the bioenvironment, a moderate biological compatibility, a suitable strength, and other properties. Therefore, it is a development tendency in current theoretical and application studies to develop a thermally sensitive shape memory polymer with low cost, excellent comprehensive properties, simple processing process, and good biocompatibility.
The betaine-type zwitterionic polymers refer to a class of polymers that have a structure similar to that of the naturally occurring betaine, and have both a cation and an anion in the same monomer structure. The commonly used sulfobetaine-type amphoteric monomers mainly include vinylpyridine derivatives, acrylamide derivatives, and (meth)acrylate derivatives. Amphoteric polymers with zero net charge and antipolyelectrolyte behavior may be obtained through homopolymerization or copolymerization of these monomers with other neutral monomers under certain conditions. The zwitterionic polymers receive great interest due to the good thermal stability, strong hydration ability, and presence of equal number of quaternary ammonium cation and sulfonate anion that are insusceptible to the pH value of the solution. The hydroxysulfobetaine has not only all the advantages of the zwitterionic compounds, but also resistance to high content of acids, bases, and salts, and good emulsifiability, dispersibility and anti-static performance, as well as microbicidal and anti-mildew effects, viscoelasticity, and others.
The use of shape memory polymers in biomedicine is always a focus of research, and the researchers in the medical and material science communities endeavor to make the medical polymer materials smart, and put them into use in the art of biomedicine. However, most of the shape memory polymers under research is required to be further improved in terms of the biocompatibility. It is found through clinical research that polyurethane shape memory polymer can cause the inflammatory response in human after long-term implantation. Therefore, there is an urgent need for developing a shape memory polymer having a good biocompatibility and superior comprehensive properties, to meet the requirement for use in clinic in biomedicine.